Glucosylceramide synthase is required for C6-ceramide nanoliposome-induced organelle stress and cell death
Sphingolipids are bioactive lipids that regulate key signaling pathways both directly as ligands and through membrane re-organization. Ceramide sits at the center of this network and is considered pro-death in many contexts, making ceramide accumulation an attractive therapeutic strategy. Given the wide-ranging regulation of cellular responses this network exerts, better understanding ceramide…
Ceramide glycosylation, a process involving the enzyme glucosylceramide synthase (GCS), has traditionally been viewed as a protective mechanism against ceramide's pro-death effects. However, a recent study challenges this notion, demonstrating that glycosphingolipids (GSLs) derived from ceramide accumulation can directly induce organelle stress and cell death.
The researchers employed ceramide nanoliposomes (CNLs) to deliver short-chain C6-ceramide to various cell types, including chronic lymphocytic leukemia (CLL) cells, all of which resulted in organelle stress and cell death. This was shown to be primarily due to the accumulation of GSLs, rather than direct ceramide action.
Pharmacologic and genetic interventions targeting GCS were found to protect multiple types of cancer cells and non-malignant embryonic kidney cells from CNL-induced death. Conversely, exogenous C8-glucosylceramide proved lethal to cells unable to degrade it.
The study elucidates a novel signaling pathway where GSL accumulation triggers an ordered series of cellular responses: lysosomal deacidification, endoplasmic reticulum stress, followed by a decline in mitochondrial respiratory capacity. These events were accompanied by MLKL phosphorylation, activation of the stress sensor JNK, and induction of CHOP. Inhibition of JNK partially mitigated the apoptotic effects.
This research not only refutes the conventional view of glycosphingolipids as a resistance mechanism but also underscores the critical role of GSL flux in ceramide-directed therapeutic strategies.
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